If you signal in advance that you are working on something, you allow others to either move on to something else so as not to duplicate the effort, or to speed up their work in order to scoop you, or to give you a call and offer to collaborate. The second option is likely to be rare and localized in a few research fields that are hugely competitive (e.g., cancer research). The first and the third options are much more likely.
I think the problem is that the researchers are doing it wrong. They are placing those announcements in wrong places using the wrong mechanism. When you go to a press release page of a University, or to Eurekalert or ScienceDaily, you expect to find press releases about the stuff that has been already done and published. The meaning of the word “published” may be completely different in 50 years, but it is not today. So, when you browse press release you expect to find only reports on published work. Seeing that a press release is about work yet to be done in the future is, of course, going to be jarring. Not because it is not nice to know what people are up to, but because they are using a wrong venue to do this – an article about an intention is masquerading as an article about a done deal.
I think researchers and their press officers need to figure out a different method and venue for publishing intentions. A blog?